In general, turbochargers serve to improve the degree of efficiency of a combustion engine and thereby increase its output. In such cases they feature a shaft that pivots in a housing of the turbocharger around a longitudinal axis and on which is arranged a turbine wheel and a compressor wheel. In this arrangement the shaft is supported to allow it to rotate by means of two radial bearings. Essentially, provision is normally made for at least one axial bearing because the exhaust gas flow impinging upon the turbine wheel produces strong axial forces that must be absorbed by means of the axial bearing.
The turbine wheel is driven by means of the exhaust gas flow of the internal combustion engine, with the compressor wheel also driven being driven here by means of the shaft. Air from the outside is compressed by means of the compressor wheel and is fed with a corresponding pressure to the cylinders of the internal combustion engine.
As a result, high demands are imposed on the support of the shaft of the exhaust gas turbocharger. The underlying reason for this is that the shaft can normally achieve very high rotational speeds of for example up to 300,000 revolutions per minute. Because of the high rotational speeds, the rotating parts of the exhaust gas turbocharger must be balanced very accurately so that as little vibration as possible is produced. In addition, the turbocharger and its bearings are subjected to high temperatures, for example by the hot exhaust gas.
A part of the damage to the axial bearings and the radial bearings is caused by the delay in the oil supply to the turbocharger after a very quick starting of the engine under cold environmental conditions.
Friction or roller bearings are used for example as bearings for the shafts. These are however subjected to considerable wear in relation to the previously described loads. The bearings and their lubrication are responsible for the majority of failures of turbochargers.